This invention relates to optical data transmission and more particularly to non return to zero (NRZ) transmission of data.
When traffic is applied to an optical transmission line in NRZ format with a high launch power (typically &gt;+18 dBm), non linear distortion is introduced by self phase modulation (SPM) causing transmission errors in the subsequent receiver at the remote end of the TX line. The distortion manifests itself by converting transitions in the data into peaks and suppressing the level of the intermediate data. Thus the receiver is more likely to detect these peaks and ignore the intermediate data. The present invention seeks to overcome or at least enable substantial reduction of errors in detection of NRZ signals.